Method of manufacturing gasket for hard disk device and gasket

ABSTRACT

The invention relates to a process for producing a gasket for hard disc equipment which is integrated with a cover member by extruding a gasket material from an extrusion orifice of a three-dimensional automatic coating controlling apparatus onto the cover member and then curing the extruded gasket material, wherein a ratio (h/w) of a height (h) of the gasket to a line width (w) of the gasket on a joint surface between the gasket and the cover member is in the range of 0.8 to 3.0 in a 80% or more portion of the gasket.

TECHNICAL FIELD

The present invention relates to a process for producing a gasket forhard disc equipment and a gasket, and more particularly to a process forproducing a gasket for hard disc equipment which serves for hermeticallysealing a joint surface between a cover body and a main body of the harddisc equipment without not only using a mold but also requiring blankingof sheets and any bonding processes, and a gasket for small-size harddisc equipment.

BACKGROUND ARTS

In recent years, in the hard disc equipment for computers, there is anincreasing tendency toward high performance and reduction in size,thereby rendering a circuit structure thereof more complicated. As aresult, since even a trace amount of dusts tends to cause failure inoperation of the hard disc equipment, it has been required uponpractical used to take any suitable dust-proofing measure. In general,gaskets are used for preventing dusts from entering into the equipment.

Conventionally, the gasket for the hard disc equipment (hereinafterreferred to merely as “HDD gasket”) has been manufactured by (1) themethod of bonding a gasket produced by blanking an urethane foam sheetor a solid rubber sheet to a cover plate; (2) the method oftransfer-molding or injection-molding a solid rubber on both surfaces ofa cover plate in the form of a bridged configuration to integrate therubber with the cover plate; (3) the dispensing method of extruding amolten resin or a solution-like resin on a surface of a cover plate intoa gasket shape by one stroke using a dispenser to thereby integrate theextruded resin with the cover plate; or (4) the method ofinjection-molding a thermoplastic elastomer blended with an adhesiveresin on a surface of a cover plate to integrate the elastomer with thecover plate.

Among these methods, the dispensing method has advantages such as (1) aprolonged lead time up to production as well as no need of a moldrequiring initial costs, and (2) no need of additional steps such asbonding step because the method enables direct formation of the gasketon a cover plate. The dispensing method has been extensively used invarious industrial application fields. In the field of the HDD gaskets,the dispensing method has been already applied to production of gasketsfor large-scale equipment such as 3.5-inch (88.9 mm) HDDs. Most of the3.5-inch HDD gaskets have been currently produced by the dispensingmethod.

On the other hand, with the progress of techniques for reduction in sizeof HDDs, 2.5-inch (63.5 mm) HDDs tend to be used as leading productsthereof, and still smaller HDDs having a size of 1.8 inch and even 1inch have also been produced and put into the market. HDD gaskets usedin these small-size HDDs are also required to have a narrower line widthand a larger height, i.e., a wall-like shape.

However, in the above dispensing method, since the gasket material isextruded from the dispenser and formed into a gasket shape by onestroke, the resultant gasket tends to be collapsed into a brokensemi-circular shape in cross section due to its own weight. For thisreason, it has been difficult to form a gasket having a narrow linewidth and a large height by the dispensing method. Further, thedispensing method as a current leading method for producing 3.5-inch HDDgaskets cannot be applied to production of 2.5-inch or smaller HDDgaskets since this method fails to attain a high accuracy in line widthand height thereof. Actually, such small-size HDD gaskets produced bythe dispensing method have not been marketed yet.

DISCLOSURE OF THE INVENTION

In view of the above problems, an object of the present invention is toprovide a process for producing a gasket for hard disc equipment whichis capable of forming a gasket having a narrow line width and a largeheight on a cover member of the equipment, and a gasket for small-sizehard disc equipment produced by the above process.

As a result of extensive researches in view of the above object, thepresent inventors have found that in the process for producing a gasketfor hard disc equipment by extruding a gasket material from an extrusionorifice of a three-dimensional automatic coating controlling apparatusonto a cover member and then curing the extruded gasket material toobtain a gasket integrated with the cover member, by extruding thegasket material to form a first-stage gasket, and then further extrudingthe gasket material on the thus formed first-stage gasket to form amulti-stage gasket, the obtained gasket has not only a narrow line widthbut also a large height.

Further, the present inventors have found that in the process forproducing a gasket for hard disc equipment by extruding a gasketmaterial from an extrusion orifice of a three-dimensional automaticcoating controlling apparatus onto a cover member and then curing theextruded gasket material to obtain a gasket integrated with the covermember, when the extrusion orifice is formed into a cross-sectionalshape selected from ellipse, semi-ellipse formed by cutting a part ofellipse along a line parallel with a minor axis of the ellipse, rhombus,quadrangle and triangle, and is rotated according to a moving directionthereof such that a minor axis of the ellipse, a straight line of thesemi-ellipse, a short diagonal line of the rhombus, a short side of thequadrangle or a base of the triangle is always kept substantiallyperpendicular to the moving direction, the resultant gasket has not onlya narrow line width but also a large height.

In addition, the present inventors have found that when the gasketbecomes insufficient in height by collapse due to its own weight, it isuseful to cure the gasket material extruded from the extrusion orificeof a nozzle as quickly as possible in a non-contact manner. Morespecifically, an activation energy ray irradiation apparatus for curingthe gasket material is disposed on a side of the extrusion orifice, andwhile forming a gasket body on the cover member by one stroke, thegasket material is immediately cured by irradiation of the activationenergy ray, thereby successfully obtaining the aimed gasket having asufficient height. Besides, the present inventors have found that whenthe gasket is extruded under a pressure of 50 kPa to 1 MPa and thegasket material used therefor has specific viscosity characteristics,the above effects can be more remarkably exhibited.

The present invention has been accomplished on the basis of thefindings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2 and 5 are conceptual views showing a gasket having amulti-stage structure according to the present invention.

FIGS. 3 and 4 are schematic views showing a gasket having a multi-stagestructure which is applied to HDD.

FIG. 6 is a conceptual view showing a shape of an extrusion orifice usedin the present invention.

FIG. 7 is a conceptual view showing an embodiment of a cross-sectionalshape of a gasket when using modified cross-section extrusion orificesaccording to the present invention.

FIG. 8 is a conceptual view showing an embodiment of a modifiedcross-section extrusion orifice as well as a cross-sectional shape of agasket obtained using the modified cross-section extrusion orifice.

FIG. 9 is a schematic views showing a gasket having a cross-sectionalshape shown in FIG. 8 which is applied to HDD.

FIGS. 10 to 12 are conceptual views showing embodiments of extrusion ofa gasket on a cover member.

FIG. 13 is a conceptual view showing a direction of movement of anextrusion orifice as well as an orientation of a nozzle when the nozzlehas an elliptical shape in cross section. In these figures, referencenumeral 1 denotes a direction of movement of an extrusion orifice; 2 isa cross-sectional shape of the extrusion orifice; 3 is a side shape ofthe extrusion orifice; 4 is a gasket; 5 is an apex of the gasket; 6 is acenter point of the gasket; 7 is the extrusion orifice; 8 is a rotationor revolution axis; 9 is an inclination of the extrusion orifice (θ°);10 is a cover plate of HDD; 11 is a dispenser nozzle; 12 is a UVirradiation apparatus; and 13 is a joint portion between the dispensernozzle and the UV irradiation apparatus.

PREFERRED EMBODIMENT TO CARRY OUT THE INVENTION

The present invention is characterized by extruding a gasket materialfrom an extrusion orifice of a three-dimensional automatic coatingcontrolling apparatus onto a cover member to form a first-stage gasket,and then further extruding the gasket material on the first-stage gasketto form a multi-stage gasket. More specifically, a second-stage gasketis formed on the first-stage gasket, if necessary, followed by forming athird-stage gasket on the second-stage gasket. The thus formed gaskethaving a multi-stage structure can exhibit a narrow line width and alarge height.

An extrusion apparatus for production of the gasket is not particularlylimited as long as the above multi-stage gasket can be produced usingthe apparatus. Examples of the extrusion apparatus include screw-typeextruders, pneumatic-type extruders and plunger-type extruders. Amongthese extruders, for example, when using a screw-type extruder, thegasket material is kneaded therein so that a structural viscosity of thegasket material is lowered due to structure breakage thereof. As aresult, even if the gasket material is kept in a stationary state afterthe extrusion, the material tends to still exhibit a low viscosity.Therefore, the height of each stage of the obtained gasket is reduced,so that a ratio (h/w) of the height (h) of the gasket to the line width(w) thereof on a joint surface to the cover member is lowered. Further,in the case where the gasket material is extruded on a lower-stagegasket that is still uncured and these stacked gasket materials arecured together at a final step, the lower-stage gasket cannot retain itsshape until the curing step. As a result, when the upper stage gasket isput on the lower-stage gasket, the resultant multi-stage gasket may failto have a sufficient height.

On the other hand, when using the pneumatic-type or plunger-typeextruder, no lowering of the structural viscosity due to structuralbreakage tends to be caused. Therefore, the use of these extruders ispreferable since the first-stage gasket tends to maintain its shape eventhough the second-stage gasket and further a third-stage gasket are putthereon.

In addition, in the process for producing the gasket for hard discequipment according to the present invention, it is preferred that thelower-stage gasket is cured before extruding the upper-stage gasketthereon. More specifically, it is preferred that after forming thefirst-stage gasket, the first-stage gasket is cured before forming thesecond-stage gasket thereon, and further the second-stage gasket iscured before forming the third-stage gasket thereon. This is because thefirst-stage gasket can be prevented from being collapsed and, therefore,can maintain a sufficient height by curing the first-stage gasket beforeextruding the second-stage gasket thereon, and similarly thesecond-stage gasket can be prevented from being collapsed and,therefore, can maintain a sufficient height by curing the second-stagegasket before extruding the third-stage gasket thereon.

In particular, when using the above screw-type extruder, it is preferredthat the first-stage gasket is cured before extruding thesubsequent-stage gasket to ensure a sufficient height of the resultantmulti-stage gasket. Meanwhile, in the case of the pneumatic-type orplunger-type extruder, it is not necessarily required to cure thefirst-stage gasket before extruding the subsequent-stage gasket, unlikethe screw-type extruder. However, in certain cases, it is advantageousto cure the first-stage gasket before extruding the subsequent-stagegasket, depending upon a viscosity of the gasket material.

Also, in the multi-stage gasket of the present invention which includesan n-stage gasket (n is an integer of 2 or more) having a length (w_(n))of an axis thereof parallel with the cover member, and a (n−1)-stagegasket having a length (w_(n−1)) of an axis thereof parallel with thecover member, the lengths (w_(n)) and (w_(n−1)) preferably satisfy therelationship represented by the formula: w_(n−1)≧w_(n) in a 80% or moreportion of the gasket. For example, this means that when n is 2 or 3, aline width (w₁) of the first-stage gasket on its joint surface to thecover member, a length (w₂) of a radius or axis of the second-stagegasket having a cross-sectional shape of circle, semi-circle, ellipse orsemi-ellipse which radius or axis extends parallel with a surface of thecover member, and further a length (w₃) of an axis of the third-stagegasket satisfy the relationship represented by the formula: w₁≧w₂≧w₃ ina 80% or more portion and preferably an entire portion of the gasket.FIG. 1 is a conceptual view showing the case where gaskets are stacked.Thus, when the gaskets are stacked, the width of the upper-stage gasketis preferably narrower than that of the lower-stage gasket since thesegaskets are hardly collapsed even when compressed. In the case of HDD,owing to the need of increasing a size of a memory disc, a thickness ofa gasket-receiving frame is very small. Therefore, if the gasket iscollapsed, there arises such a problem that the gasket is offset fromthe frame and no longer act as a seal. From the above viewpoints, it ismore preferred to establish the relationship represented by the formula:w_(n−1)/w_(n)>1.1.

Meanwhile, in the case of HDD, one disc or a plurality of discs aredisposed at a center thereof. Therefore, when using the gasketsatisfying the above width relationship, the HDD is prevented fromsuffering from disadvantages such as failure in rotation of discs due tothe gasket and defective reading or writing, which results in productionof HDD having a good operability.

In addition, the n-stage gasket (n is an integer of 2 or more)preferably has a cross-sectional shape of either circle, semi-circle,ellipse or semi-ellipse, and a center point of the cross section of then-stage gasket is preferably located more outside than a center point ofthe cross section of the (n−1)-stage gasket relative to a center of thecover member. FIGS. 2 to 4 are conceptual views showing a gasket havinga multi-stage structure when n is 3. More specifically, FIG. 2schematically show such a multi-stage structure in which the centerpoint of cross section of an upper-stage gasket is more offset toward anoutside of the cover member than that of a lower-stage gasket; FIG. 3schematically shows the case where the gasket is applied to actual HDD;and FIG. 4 schematically shows the case where the center points of therespective stage gaskets are aligned with each other along the directionperpendicular to the cover member. The structures as shown in FIGS. 2and 3 are advantageous since the obtained HDD is prevented fromsuffering from defects such as failure in rotation of discs due to thegasket and errors of reading or writing.

Further, when the gasket material is extruded using the dispenser with anozzle having a modified cross-sectional shape, in order to achieve therequirement of w₁≧w_(n)≧w_(n+1), it is effective to establish therelationship represented by the formula: S₁≧S_(n)≧S_(n+1) wherein S₁ isa cross-sectional area of the first-stage gasket; S_(n) is across-sectional area of the n-stage gasket, thereby obtaining a stablegasket. More specifically, as shown in FIG. 5, it is preferable tosatisfy the formula: S₁≧S₂≧S₃ wherein S₂ is a cross-sectional area ofthe second-stage gasket; and S₃ is a cross-sectional area of thethird-stage gasket.

Next, the present invention is characterized in that the extrusionorifice of the three-dimensional automatic coating controlling apparatushas a modified non-circular cross-sectional shape having a major axisand a minor axis, and the minor axis is always kept substantiallyperpendicular to a moving direction of the extrusion orifice. Thenon-circular shape having a major axis and a minor axis includes, asshown in FIG. 6, ellipse, semi-ellipse formed by cutting a part ofellipse along a line parallel with a minor axis thereof, rhombus,quadrangle such as rectangle and trapezoid, triangle and other polygonalshapes, and the minor axis means a minor axis of ellipse, a straightline of semi-ellipse, a short diagonal line of rhombus, a short side ofrectangle, a base of trapezoid, a base of triangle, a base of therespective polygonal shapes, etc. To always keep the minor axis such asa minor axis of ellipse, a straight line of semi-ellipse, a short sideof quadrangle and a base of triangle substantially perpendicular to themoving direction of the extrusion orifice, there may be used variousmethods. For example, in the case where a nozzle constituting theextrusion orifice is arranged rotatably, and the gasket is formed by onestroke, the nozzle is rotated about a axis perpendicular to the covermember at non-linear portions of the gasket to be formed such as cornerand curved portions according to the moving direction of the extrusionorifice. The above mechanism enables production of a gasket having anarrow line width and a large height.

The cross-sectional shape of the extrusion orifice is preferably formedsuch that the ratio (c/d) of a major axis (c) to a minor axis (d) of aelliptical or semi-elliptical cross-sectional shape exceeds 1.1; theratio (e/f) of a long diagonal line (e) to a short diagonal line (f) ofa rhombic cross-sectional shape exceeds 1.1; the ratio (g/i) of a longside (g) to a short side (i) of a rectangular cross-sectional shapeexceeds 1.1; and the ratio (j/k) of a height (j) to a long side (k)(among two parallel sides) of a trapezoidal cross-sectional shapeexceeds 1.1. The triangular cross-sectional shape is preferably anisosceles triangle having an apex angle of less than 90°. Thus, byrotating the extrusion orifice according to the moving directionthereof, and always keeping the minor axis of cross section of theextrusion orifice such as a minor axis of ellipse, a straight line ofsemi-ellipse, a short diagonal line of rhombus, a short side ofquadrangle and a base of triangle substantially perpendicular to themoving direction thereof, the resultant gasket can exhibit not only anarrow line width but also a large height. In addition, at the tip endof the extrusion orifice, the straight line of semi-ellipse, the shortside of quadrangle or the base of triangle is preferably located forwardrelative to the moving direction so as to allow the extruded gasket tocome into contact with the cover member at an end portion of ellipse, astraight line of semi-ellipse, a short side of quadrangle or a base oftriangle thereof in advance, and adhere or bond thereto. In particular,in the case of the extrusion orifice having an ellipticalcross-sectional shape, when the ratio (c/d) exceeds 1.1, it is possibleto readily produce a gasket having a ratio (h/w) of more than 0.8.

The thus produced gasket has a cross-sectional shape with a narrow linewidth and a large height as shown in the conceptual view of FIG. 7. Inthis case, the cross-sectional shape of the obtained gasket is notnecessarily symmetrical. Namely, in one preferred embodiment of thepresent invention, an extrusion orifice having a cross-sectional shapeas shown in FIG. 8 may be used to produce a gasket having across-sectional shape as also shown in FIG. 8. More specifically, thegasket as shown in FIG. 8 has such a configuration that the apex ofcross section thereof is offset toward outside of the cover memberrelative to a center of a gasket portion contacting the cover member.FIG. 9 shows a schematic view in which the gasket having thecross-sectional shape as shown in FIG. 8 is applied to actual HDD. Thisarrangement has such an advantage that the obtained HDD is free fromdefects such as failure in rotation of discs due to the gasket, anderrors of reading or writing.

The above cross-sectional shape of the extrusion orifice can be obtainedby forming an orifice of a nozzle into the aimed cross-sectional shapeduring production process of the extrusion orifice. In addition, a tipend of the nozzle having a circular cross section may be cut obliquelyto produce a substantially elliptical or semi-elliptical shape relativeto the cover member. This method has such an advantage that a modifiedcross-section extrusion orifice can be produced in a convenient mannerwith a good reproducibility, because an extrusion orifice having acircular shape is readily available, and the extrusion orifice isreadily cut obliquely.

Next, the three-dimensional automatic coating controlling apparatus maybe provided, if required, with a mechanism for inclining the extrusionorifice in the forward/rearward direction and rightward/leftwarddirection relative to a surface of the cover member and the movingdirection of the extrusion orifice. The provision of such a mechanismallows an extrusion position of the gasket extruded as well as a shapeof the extruded gasket to be accurately and precisely controlled. FIGS.10 to 12 are conceptual views showing the extrusion orifice of thethree-dimensional automatic coating controlling apparatus. As shown inFIG. 10, the extrusion orifice can be disposed at an angle θ of 90°relative to the cover member upon extrusion of the gasket. In this case,the nozzle is rotated about a axis perpendicular to the cover member tothereby allow the gasket to be extruded into a desired shape by onestroke. Also, as shown in FIG. 11, the extrusion orifice can be inclinedin the forward direction relative to the moving direction thereof suchthat the angle θ is less than 90° upon extrusion of the gasket. In thiscase, the nozzle is also preferably revolved about the axisperpendicular to the cover member. Further, as shown in FIG. 12, uponextrusion of the gasket, the extrusion orifice may be inclined in aplane making an angle of 90° relative to the moving direction thereofsuch that the angle θ is less than 90°. In the above case, the nozzle isalso revolved about the axis perpendicular to the cover member.

In the HDD gasket of the present invention, the ratio (h/w) of theheight (h) of the gasket to the line width (w) thereof on its jointsurface to the cover member is preferably in the range of 0.8 to 3.0 andmore preferably more than 0.8 in a 80% or more portion and preferably anentire portion of the gasket. When the ratio (h/w) is 0.8 or more, theeffects of the present invention can be sufficiently achieved. On theother hand, when the ratio (h/w) is 3.0 or lower, the obtained gaskettends to become uncollapsable when compressed and, therefore, is freefrom sealing problems.

Also, the extrusion pressure used for production of the gasket ispreferably in the range of 50 kPa to 1 MPa. When the extrusion pressurelies within the above-specified range, the gasket material can beextruded at a high efficiency without collapse thereof, therebyobtaining a gasket having a sufficiently narrow line width and a largeheight. From these viewpoints, the extrusion pressure upon production ofthe gasket is more preferably 80 to 800 kPa, still more preferably 100to 800 kPa and most preferably 200 to 800 kPa.

The thus extruded gasket tends to undergo sagging or drawdown at anacute apex thereof as well as collapse near to a bottom thereof due toits own weight. As a result, in these cases, the obtained gasket hassuch a cross-sectional shape formed by cutting an ellipse along a lineparallel with a minor axis of the ellipse. The exact cross-sectionalshape of the finally obtained gasket may be determined according to ashape of the extrusion orifice, a discharge velocity of the gasketmaterial, a moving velocity of the discharge port, viscoelasticcharacteristics of the gasket material, etc.

Meanwhile, an apparatus used for extrusion of the gasket is notparticularly limited as long as the above extrusion pressure is attainedthereby. However, for example, in the case of the screw-type extruder,the gasket material is kneaded therein. As a result, a structuralviscosity of the gasket material tends to be lowered owing to structuralbreakage upon kneading, and the extruded gasket material tends to beflowed away even when kept in a stationary state after the extrusion,resulting in lowering of the ratio h/w of the resultant gasket. On theother hand, the use of the pneumatic-type extruder is more advantageous,since the gasket material tends to be free from lowering of thestructural viscosity due to structural breakage thereof, so that theresultant gasket tends to maintain its shape.

Further, the use of a ram-type or a plunger-type extruder which extrudesthe gasket material by applying a mechanical pressure thereto is alsoeffective like the pneumatic-type extruder, since it is also free fromlowering of the structural viscosity due to the structural breakage.

In the process for production of the gasket for hard disc equipmentaccording to the present invention, there may be used various methodsfor curing the gasket material. Among these methods, there is preferablyused the method of irradiating the molded gasket with an activationenergy ray in a necessary amount capable of sufficiently curing thegasket material, from an activation energy ray irradiation apparatus.

The activation energy ray used for curing the gasket material includesan ultraviolet light, and ionizing radiation such as an electron beam,a-ray, β-ray and γ-ray. Of these energy rays, especially preferred is anultraviolet light since an apparatus therefor is simple and easy to use,and the ultraviolet light can effectively cure the gasket material.Also, when the ultraviolet light is used, it is preferred to add aphotopolymerization initiator and/or a photo-sensitizer to the gasketmaterial. On the contrary, when the ionizing radiation such as electronbeam and γ-ray is used, the gasket material can be rapidly cured withoutadding the photopolymerization initiator and/or photo-sensitizerthereto.

Examples of a light source for irradiating the ultraviolet light includeelectrode-type light sources such as a metal halide lamp, a xenon lamp,a low-pressure mercury lamp, a high-pressure mercury lamp and anultrahigh-pressure mercury lamp, and electrodeless light sources such asan excimer lamp and a metal halide lamp. The atmosphere in which theultraviolet light is irradiated is preferably an inert gas atmospheresuch as nitrogen gas and carbon dioxide gas or an atmosphere having areduced oxygen concentration. However, an ultraviolet-curable gasketmaterial can be sufficiently cured even in an ordinary atmospheric air.The temperature of the atmosphere upon irradiation of the ultravioletlight is usually in the range of 10 to 200° C.

Further, there is preferably used the method in which the gasketmaterial is cured by the ultraviolet light irradiated from anultraviolet light irradiation apparatus simultaneously with extrusion ofthe gasket material from the extrusion orifice onto the cover member tointegrate the gasket material with the cover member. In this method,since the time required from extrusion to curing of the gasket materialis short, the gasket material can be cured without deformation of ashape thereof upon extrusion. Further, the ultraviolet light irradiationapparatus is preferably controlled so as to be moveable in associationwith the movement of the extrusion orifice of the three-dimensionalautomatic coating controlling apparatus. In this case, if theultraviolet light impinges against the extrusion orifice, the gasketmaterial contained therein is cured. Therefore, the ultraviolet light ispreferably irradiated on the extruded gasket material so as to follow alocus of passage of the extrusion orifice while preventing theultraviolet light from impinging against the extrusion orifice. Forexample, as shown in FIG. 13, there may be used the method in which theextrusion orifice is coupled with an ultraviolet irradiation outlet tobe spaced by a given distance apart from each other to such an extentthat the ultraviolet light irradiated is not interfered with theextrusion orifice, and the gasket material is extruded and then curedwhile rotating a line connecting between centers of the ultravioletirradiation outlet and the extrusion orifice so as to be substantiallyaligned with the moving direction.

In the case of the modified cross-section extrusion orifice havingvarious non-circular cross sectional shapes (such as flattened extrusionorifice), since the extrusion orifice is required to rotate in analigned relation to the moving direction, the activation energy rayirradiation outlet can be fixedly coupled to the extrusion orifice toallow the ultraviolet light to be irradiated to an optimum position inassociation with the movement of the extrusion orifice. In this case, itis preferred that after stopping extrusion of the gasket material, onlythe ultraviolet light is finally irradiated so as to follow the gasketportion as formed, thereby curing the gasket. Meanwhile, in the presentinvention, there may be used a modified apparatus of a commerciallyavailable coating apparatus constituted of a three-dimensional automaticcoater equipped with a rotating device. If an irradiation range of theactivation energy ray is too narrow, small curvature portions may failto be surely irradiated with the activation energy ray. Therefore, theultraviolet light irradiated preferably has a width of about 5 to 15 mmin the direction perpendicular to the moving direction. In addition, inorder to apply a sufficient curing energy to the gasket material, theultraviolet light preferably has a sufficient intensity and width.

When the ultraviolet light is irradiated in the above-described manner,there is obtained such an advantage that even the gasket material havinga low yield value and a poor shape retention can be rapidly curedimmediately after being extruded without breakage of a shape thereof.Further, when the gasket material is extruded into a multi-stagestructure, it is possible to readily produce a gasket having a ratio(h/w) of 0.8 or more, i.e., a narrow width and a large height.

The gasket material used in the present invention may be appropriatelyselected from various materials according to production conditions ofthe gasket. Specific examples of the gasket material include thosematerials exhibiting a viscosity of preferably 50 to 1,000 Pa·s and morepreferably 80 to 700 Pa·s at a shear rate of 1.0/s at a moldingtemperature thereof. The gasket material having a viscosity of 50 to1,000 Pa·s exhibits a good fluidity and, therefore, can retain a gasketshape and is readily moldable into a desired gasket.

Meanwhile, the molding temperature of the gasket material is preferablyin the range of 30 to 140° C. and more preferably 40 to 120° C.

Also, when a common logarithm (y) of the viscosity (Pa·s) and a commonlogarithm (x) of the shear rate (s⁻¹) as measured at the moldingtemperature of the gasket is represented by the formula: y=−ax+b whereina and b are positive numbers, the a value is preferably 0.2 or more,more preferably 0.25 or more and most preferably 0.35 or more. When thea value is less than 0.2, a shear rate dependency of the viscosity issmall, so that the viscosity of the gasket material becomes too low,resulting in poor shape retention, or the viscosity of the gasketmaterial becomes too high, resulting in inconvenience such as failure inextrusion of the gasket material.

Further, a so-called Casson plot obtained by plotting an one-secondpower of shear rate and an one-second power of shear stress measuredwhile varying the shear rate on rectangular coordinates is used forevaluation of a yield value of the viscosity. The yield value isobtained as the second power of an intercept at which a line obtained byapproximating the plots by least square method intersects the axis ofthe one-second power of shear stress, and is used as an index forevaluating a shape retention of the gasket material maintained in astationary state after the extrusion and application thereof. The yieldvalue exceeding 5 Pa enables production of a multi-stage gasket having aratio (h/w) of 0.8 or more by the method of extruding and curing theupper-stage gasket after curing the lower-stage gasket. In addition, theyield value exceeding 30 Pa is more preferred because the second-stagegasket can be extruded before the first-stage gasket extruded is cured,and then the first-stage and second-stage gaskets can be cured togethersimultaneously. Further, from the above viewpoints, the yield value ofthe gasket material is more preferably 70 Pa or more. Also, in the casewhere the gasket is molded while rotating the above modifiedcross-section extrusion orifice, the yield value of the gasket materialis preferably 30 Pa or more and more preferably 70 Pa or more.

As described above, the material having a high thixotropic property anda high shear rate dependency exhibits a low viscosity upon extrusion,and a high viscosity in a stationary state after the extrusion and,therefore, is a suitable gasket material since the resultant gasket isfree from breakage of a shape thereof.

In the case of the screw-type extruder, as described above, since thegasket material is kneaded therein, the structural viscosity thereof islowered owing to structural breakage, so that the viscosity of thegasket material kept in s stationary state tends to be lowered. For thisreason, the use of the pneumatic-type or plunger-type extruder is morepreferred.

Meanwhile, in order to control the viscosity of the gasket material andthe relation between the viscosity and shear rate thereof to theabove-specified ranges, there may be used the method of dispersing aninorganic filler therein, the method of blending an organic thickeningagent therein, the method of controlling a molecular weight of apolymerizable oligomer used therein, the method of controlling apolarity of the material, etc. Examples of the inorganic filler usablein the above method include wet silica and dry silica which may or maynot be rendered hydrophobic with silane-based coupling agents, siliconeoil, modified silicone oil, sodium fluoride, magnesium silicofluoride,nonionic surfactants and synthetic polyethylene waxes, as well asbentonite, mica and synthetic smectite which may or may not be treatedwith a quaternary ammonium salt. Examples of the organic thickeningagent include hydrogenated castor oil, amide waxes and polyethyleneoxide.

Next, the gasket material has a hardness of 50° or lower and preferably40° or lower as measured by a durometer A-type hardness test accordingto JIS K 6253. When the hardness is 50° or lower, the gasket tends to bedeformed when assembling a cover with the gasket into a main body of theHDD. As a result, the cover is prevented from being flexed, so that asealability of the HDD can be retained without damage thereto.

Further, in order to ensure a sealability of the gasket for HDD that isexpected to be mounted to automobiles, the gasket material preferablyhas a permanent strain of 20% or lower and more preferably 10% or lowerwhen measured after compressing the gasket material by 25% at 100° C.and then allowing the material to stand for 24 h. Meanwhile, in order toprevent contamination of the hard disc, a total amount of gasesgenerated from the gasket material upon heating as well as an amount ofsiloxane generated therefrom are preferably controlled to a low level.In addition, the gasket material preferably has a low moisturepermeability in order to prevent penetration of water vapor into theHDD.

In the present invention, when using the gasket material having theabove-specified properties, it is possible to obtain a gasket having anarrow line width and a large height. For example, if the line width ofthe obtained gasket is 1.0 mm, the height thereof is as large as 0.5 to2.0 mm.

The gasket material used in the present invention is not particularlylimited as long as the material has the above-specified properties. Inparticular, the gasket material preferably contains, as a maincomponent, at least one material selected from the group consisting ofurethanes, epoxy-based polymers, silicone, polyisoprene, hydrogenatedpolyisoprene, polybutadiene, hydrogenated polybutadiene,polyisobutylene, fluorine-containing rubbers and modified productsthereof.

Of these gasket materials, most preferred are those materials containingacrylic-modified urethanes as a main component. Examples of theacrylic-modified urethanes include urethane acrylate oligomers ofpolyether polyols, urethane acrylate oligomers of polyester polyols,urethane acrylate oligomers containing both ether and ester groups in amolecule thereof, and urethane acrylate oligomers of carbonate diolscontaining a carbonate group. Examples of the polyether polyols includepolyethylene glycol, polypropylene glycol, polytetramethylene glycol,polyhexamethylene glycol, and addition compounds obtained by addingethyleneoxide or propyleneoxide to 1,3-butylene glycol, 1,4-butyleneglycol, 1,6-hexane diol, neopentyl glycol, cyclohexane dimethanol,2,2-bis(4-hydroxycyclohexyl)propane, bisphenol A, etc. The polyesterpolyols may be produced by reacting an alcohol component with an acidcomponent. Examples of the alcohol component include polyethyleneglycol, polypropylene glycol, polytetramethylene glycol, and additioncompounds obtained by adding ethyleneoxide or propyleneoxide to1,3-butylene glycol, 1,4-butylene glycol, 1,6-hexane diol, neopentylglycol, 1,4-cyclohexane dimethanol, 2,2-bis(4-hydroxycyclohexyl)propane,bisphenol A, etc., or addition compounds obtained by addingε-caprolactone thereto. Examples of the acid component include dibasicacids such as adipic acid, sebacic acid, azelaic acid and dodecanedicarboxylic acid, and anhydrides thereof. As the polyester polyols,there may also be used compounds obtained by reacting the alcoholcomponent, the acid component and ε-caprolactone with each other at thesame time. The carbonate diols may be produced, for example, bytransesterification reaction of diaryl carbonates or dialkyl carbonatessuch as diphenyl carbonate, bis-chlorophenyl carbonate, dinaphthylcarbonate, phenyltoluyl carbonate, phenyl-chlorophenyl carbonate,2-tolyl-4-tolyl carbonate, dimethyl carbonate and diethyl carbonate withdiols such as 1,6-hexane diol, neopentyl glycol, 1,4-butane diol,1,8-octane diol, 1,4-cyclohexane dimethanol, 2-methylpropane diol,dipropylene glycol and dibutylene glycol, reaction products of the abovediol compounds with dicarboxylic acids such as oxalic acid, malonicacid, succinic acid, adipic acid, azelaic acid and hexahydrophthalicacid, or polyester diols as reaction products of ε-caprolactone. Thethus obtained carbonate diols may be in the form of a monocarbonate diolcontaining one carbonate structural unit in a molecule thereof, or apolycarbonate diol containing two or more carbonate structural units ina molecule thereof. The especially preferred acrylic-modified urethanescontained in the gasket material used in the present invention areurethane acrylate oligomers of polyether polyols and polyester polyols.Examples of especially preferred organic diisocyanates used forproduction of the above urethanes include, but are not particularlylimited to, methylene diisocyanate, tolylene diisocyanate, isophoronediisocyanate, 4,4′-dicyclohexylmethane diisocyanate and hexamethylenediisocyanate.

The gasket material used in the present invention may also contain knownphotopolymerization initiators. Examples of the photopolymerizationinitiators include intramolecular cleavage-type photopolymerizationinitiators e.g., benzoin alkyl ether-based compounds such as benzoinethyl ether, benzoin isobutyl ether and benzoin isopropyl ether;acetophenone-based compounds such as 2,2-diethoxyacetophenone and4′-phenoxy-2,2-dichloroacetophenone; propiophenone-based compounds suchas 2-hydroxy-2-methylpropiophenone,4′-isopropyl-2-hydroxy-2-methylpropiophenone and4′-dodecyl-2-hydroxy-2-methylpropiophenone; benzyldimethyl ketal,1-hydroxycyclohexyphenyl ketone, and anthraquinone-based compounds suchas 2-ethyl anthraquinone and 2-chloroanthraquinone; and acyl phosphineoxide-based compounds; as well as other hydrogen abstraction-typephotopolymerization initiators such as benzophenone/amine-basedcompounds; Michler's ketone/benzophenone-based compounds;thioxanthone-based compounds; and amine-based compounds. In addition,non-extraction-type photopolymerization initiators may also be used toavoid migration of unreacted photopolymerization initiators. Examples ofthe non-extraction-type photopolymerization initiators includehigh-molecular compounds produced from acetophenone-based initiators,and compounds obtaining by adding an acrylic double bond tobenzophenone.

These photopolymerization initiators may be used singly or in thecombination of any two or more thereof. The amount of thephotopolymerization initiator blended is preferably 0.5 to 5 parts bymass and more preferably 1 to 3 parts by mass based on 100 parts by massof the acrylic-modified urethanes as an main component of the gasketmaterial.

The gasket material used in the present invention may further containphotosensitizers, thermal polymerization inhibitors, curingaccelerators, pigments, etc., unless the addition thereof adverselyaffects the effects of the present invention.

The cover member that is integrated with the gasket produced byextruding and curing the gasket material may be made of metals orsynthetic resins such as thermoplastic resins. Examples of the metalsused for the cover member include nickel-plated aluminum, nickel-platedsteel, cold-rolled steel, zinc-plated steel, aluminum/zinc alloy-platedsteel, stainless steel, aluminum, aluminum alloys, magnesium andmagnesium alloys. The metals for the cover member may be appropriatelyselected from these materials. Further, in the present invention,injection-molded magnesium may also be used as the cover member. In viewof good corrosion resistance, nickel-electroless plated metals aresuitably used. In the present invention, of these nickel-electrolessplated metals, preferred are nickel-plated aluminum and nickel-platedsteel. In the present invention, there may be used knownnickel-electroless plating methods that are applicable to conventionalmetal materials, for example, the method of dipping a metal plate in anickel-electroless plating bath composed of an aqueous solutioncontaining an appropriate amount of nickel sulfate, sodiumhypophosphite, lactic acid, propionic acid, etc., and having a pH ofabout 4.0 to 5.0 at a temperature of about 85 to 95° C.

Examples of the thermoplastic resins used for the cover member includestyrene-based resins such as acrylonitrile/styrene (AS) resins,acrylonitrile/butadiene/styrene (ABS) resins, polystyrene andsyndiotactic polystyrenes, olefin-based resins such as polyethylene,polypropylene and polypropylene composites, e.g., ethylene-propylenecopolymers, polyamide-based resins such as nylon, polyester-based resinssuch as polyethylene terephthalate and polybutylene terephthalate, andother thermoplastic resins such as modified polyphenylene ethers,acrylic resins, polyacetals, polycarbonates, liquid crystal polymers andpolyphenylene sulfides (PPS). The thermoplastic resin for the covermember may be appropriately selected from these compounds. The liquidcrystal polymers are preferably thermotropic liquid crystal polymers,and specific examples thereof include polycarbonate-based liquid crystalpolymers, polyurethane-based liquid crystal polymers, polyamide-basedliquid crystal polymers and polyester-based liquid crystal polymers.These resins may be used singly or in the combination of any two or morethereof.

In order to enhance adhesion between the cover member and the gasket,the surface of the cover member may be previously treated. Examples ofthe surface treatment include plasma treatment and corona dischargetreatment. The plasma treatment may be performed using, for example, aplasma irradiation apparatus available from Keyence Corp.

Meanwhile, upon production of the gasket, in some cases, the gasket isformed with protrusions at not only an outer peripheral portion but alsoan inner peripheral portion thereof. In such a case, the process forproducing the gasket according to the present invention may be used incombination with the other molding methods. That is, the outerperipheral portion of the gasket may be produced by the extrusionprocess of the present invention, whereas the protrusions at the innerperipheral portion may be formed by the other molding methods. Thisprocedure is effective in the cases where the inner protrusions arehardly moldable by the extrusion method, where a very high accuracy isrequired, where a high adhesion force is required, where materialproperties unavailable from extrudable materials are required, etc.Examples of the other molding methods include the method of directlyinjection-molding a thermoplastic rubber or a thermosetting rubber ontothe cover member, the method of bonding previously formed protrusions tothe gasket by a bonding agent or an adhesive, etc. When the protrusionsare formed by the injection-molding method, the cover member may bepreviously coated with an adhesive, or an adhesive rubber may beinjection-molded onto the cover member.

The present invention will be described in more detail below withreference to the following examples. However, these examples are onlyillustrative and not intended to limit the invention thereto.

Gasket Production Apparatus

(1) Three Dimensional Automatic Coating Controlling Apparatus

As the three-dimensional automatic coating controlling apparatus, therewere used “CENTURY C720” available from NORDSON Inc. (hereinafterreferred to as “apparatus 1”), and “Custom-Built Shot Master 3”available from Musashi Engineering Co., Ltd. (hereinafter referred to as“apparatus 2”). The apparatus 1 is a screw-type extruder, and theapparatus 2 is usable as either a screw-type or pneumatic-type extruder.In the Examples and Comparative Examples, the apparatus 2 was used as apneumatic-type extruder. In these extruders, a replaceable extrusionorifice having a circular shape was used upon the extrusion. The size ofa nozzle used in these apparatuses is represented by an inner diameterthereof in Table 1.

(2) Ultraviolet-Curing Apparatus

“UV1501BA-LT” available from Sen Engineering Co., Ltd., was used.

Gasket Materials

(1) PU#1: Ultraviolet-curable urethane containing an acrylic-modifiedether-based urethane to which silica was added to impart a thixotropicproperty thereto. In addition, PU#1 exhibited a viscosity of 251 Pa·s asmeasured at 50° C. and a shear rate of 1.0/s, a relationship representedby the formula: y=−0.544x+2.399 wherein y is a common logarithm of theviscosity (Pa·s) and x is a common logarithm of the shear rate (s⁻¹),and a yield value of 110 Pa as determined from a Casson plot thereof at50° C.

(2) PU#2: Ultraviolet-curable urethane containing an acrylic-modifiedether-based urethane which had no thixotropic property because of noaddition of the filler thereto. In addition, PU#2 exhibited a viscosityof 80 Pa·s as measured at 50° C. and a shear rate of 1.0/s, arelationship represented by the formula: y=−0.01x+1.64 wherein y is acommon logarithm of the viscosity (Pa·s) and x is a common logarithm ofthe shear rate (s⁻¹), and a yield value as low as 0.25 Pa as measured at50° C. from Casson plot thereof.

Viscosity-Measuring Method

Using “Rheo Stress R150” available from HAAKE Inc., a sample was placedbetween parallel discs spaced by a distance of 0.2 mm apart from eachother. The apparatus was rotated at a given temperature and a givenshear stress, and a shear rate was determined from the number ofrevolution thereof. Further, the shear stress was divided by the shearrate to calculate the viscosity.

EXAMPLE 1

The gasket material PU#1 was applied onto a 0.4 mm-thick nickel-platedaluminum plate of a 2.5-inch HDD under the conditions shown in Table 1using the above apparatus 1, and then cured using an ultraviolet curingapparatus, thereby forming a first-stage gasket. Next, the same gasketmaterial was extruded onto the first-stage gasket under the sameconditions, and then cured using the ultraviolet curing apparatus,thereby forming a second-stage gasket. Meanwhile, in Table 1, the numberof application “2” means that the gasket material was applied twice toform the first-stage and second-stage gaskets, and the number of curing“2” means that the first-stage and second-stage gaskets wererespectively cured.

The details of a shape of the thus obtained gasket are shown in Table 2.As a result, it was confirmed that a good gasket having a ratio h/w of1.0 was produced.

EXAMPLE 2

The gasket material PU#1 was applied onto a 0.4 mm-thick nickel-platedaluminum plate of a 2.5-inch HDD under the conditions shown in Table 1using the above apparatus 2 to form a first-stage gasket. Next, the samegasket material was extruded onto the first-stage gasket under the sameconditions to form a second-stage gasket, and then both the first-stageand second-stage gaskets were cured using an ultraviolet curingapparatus. Meanwhile, in Table 1, the number of application “1” meansthat after respectively applying the first-stage and second-stagegaskets, both the gaskets were cured at one time.

The details of a shape of the thus obtained gasket are shown in Table 2.As a result, it was confirmed that when the gasket material waspneumatically extruded using the apparatus 2, a good gasket having aratio h/w of 1.7 was produced nevertheless the first-stage gasket wasnot cured after the application thereof. This was because thefirst-stage gasket underwent no shearing force upon extrusion thereofand, therefore, was free from deterioration in its viscosity, and had ahigh shape retention property.

EXAMPLE 3

The same procedure as in EXAMPLE 2 was repeated except that thefirst-stage gasket was cured using the ultraviolet curing apparatusafter application thereof but before forming the second-stage gasketthereon, thereby forming a gasket. The details of a shape of the thusobtained gasket are shown in Table 2. As a result, it was confirmed thatthe thus obtained gasket was further enhance in ratio h/w compared tothat obtained in EXAMPLE 2.

COMPARATIVE EXAMPLE 1

The gasket material PU#2 was applied onto a 0.4 mm-thick nickel-platedaluminum plate of a 2.5-inch HDD under the conditions shown in Table 1using the apparatus 2, and then cured using an ultraviolet curingapparatus, thereby forming a gasket. The details of a shape of the thusobtained gasket are shown in Table 2.

As a result, it was confirmed that when the gasket material waspneumatically extruded under an air pressure of 330 kPa at an ordinarytemperature, the material applied was spread around and had a ratio h/wlow as 0.5, thereby failing to obtain a good gasket.

COMPARATIVE EXAMPLE 2

The gasket material PU#2 was applied onto a 0.4 mm-thick nickel-platedaluminum plate of a 2.5-inch HDD under the conditions shown in Table 1using the apparatus 2 to form a first-stage gasket. Next, the samegasket material was extruded onto the first-stage gasket under the sameconditions to form a second-stage gasket, and then both the first-stageand second-stage gaskets were cured using an ultraviolet curingapparatus. The details of a shape of the thus obtained gasket are shownin Table 2.

As a result, it was confirmed that even when the first-stage andsecond-stage gaskets were stacked together under the above conditions,the ratio h/w was as low as 0.73, thereby failing to obtain a goodgasket.

COMPARATIVE EXAMPLE 3

The gasket material PU#1 was applied onto a 0.4 mm-thick nickel-platedaluminum plate of a 2.5-inch HDD under the conditions shown in Table 1using the apparatus 1, and then cured using an ultraviolet curingapparatus, thereby forming a gasket. The details of a shape of the thusobtained gasket are shown in Table 2.

COMPARATIVE EXAMPLE 4

The gasket material PU#1 was applied onto a 0.4 mm-thick nickel-platedaluminum plate of a 2.5-inch HDD under the conditions shown in Table 1using the apparatus 2, and then cured using an ultraviolet curingapparatus, thereby forming a gasket. The details of a shape of the thusobtained gasket are shown in Table 2.

COMPARATIVE EXAMPLE 5

The gasket material PU#1 was applied onto a 0.4 mm-thick nickel-platedaluminum plate of a 2.5-inch HDD under the conditions shown in Table 1using the apparatus 1, and then cured using an ultraviolet curingapparatus, thereby forming a gasket. The details of a shape of the thusobtained gasket are shown in Table 2. TABLE 1-1 Three- Inner Examplesdimensional diameter and automatic Shape of of Comparative Gasketcontrolling Extrusion extrusion Extrusion Examples material apparatusmethod orifice orifice Example 1 PU#1 Apparatus 1 Screw Circular φ1.25Example 2 PU#1 Apparatus 2 Pneumatic Circular φ1.1 Example 3 PU#1Apparatus 2 Pneumatic Circular φ1.1 Comparative PU#2 Apparatus 2Pneumatic Circular φ1.25 Example 1 Comparative PU#2 Apparatus 2Pneumatic Circular φ1.25 Example 2 Comparative PU#1 Apparatus 1 ScrewCircular φ1.25 Example 3 Comparative PU#1 Apparatus 2 Pneumatic Circularφ1.25 Example 4 Comparative PU#1 Apparatus 1 Screw Circular φ1.25Example 5

TABLE 1-2 Examples and Extrusion Temperature of Comparative pressuregasket material Number of Number of Examples (kPa) (° C.) applicationcuring Example 1 — Ordinary 2 2 temperature Example 2 450 55 2 1 Example3 450 55 2 2 Comparative 330 Ordinary 1 1 Example 1 temperatureComparative 330 Ordinary 2 1 Example 2 temperature Comparative —Ordinary 1 1 Example 3 temperature Comparative 380 55 1 1 Example 4Comparative — 55 2 1 Example 5

TABLE 2 Examples and Shape of gasket Comparative Cross-sectional Height(h) Line width Examples shape (mm) (w) (mm) h/w Example 1Semi-circular + elliptical 2 2 1 Example 2 Semi-elliptical + circular1.5 0.9 1.7 Example 3 Semi-elliptical + circular 1.6 0.9 1.8 ComparativeSemi-circular 1 2 0.5 Example 1 Comparative Semi-elliptical 1.6 2.2 0.73Example 2 Comparative Semi-circular 1 2 0.5 Example 3 ComparativeSemi-elliptical 1.1 1.4 0.79 Example 4 Comparative Semi-circular 1.6 2.50.6 Example 5

EXAMPLE 4

The gasket material PU#1 was applied onto a 0.4 mm-thick nickel-platedaluminum plate of a 2.5-inch HDD using the apparatus 2, and then curedusing an ultraviolet curing apparatus. While rotating a nozzle having anelliptical cross-sectional shape (1.1×1.8 mm) such that a minor axis ofthe nozzle was always kept in a direction substantially perpendicular toa moving direction of an extrusion orifice thereof, namely a longerdiameter (major axis) of the ellipse was always substantially alignedwith the moving direction as shown in FIG. 6, the gasket material wasextruded under the conditions shown in Table 3, thereby obtaining agasket. The details of a shape of the thus obtained gasket are shown inTable 4.

As shown in Table 4, it was confirmed that the method used in EXAMPLE 4enabled production of a gasket having a semi-elliptical cross sectionand a ratio h/w of 1.5 which was uniformly formed over an entireperipheral portion of the aluminum plate.

EXAMPLE 5

The same procedure as in EXAMPLE 4 was repeated except that a nozzlehaving an elliptical cross section (1.1×1.5 mm) was used, therebyobtaining a gasket. The details of a shape of the thus obtained gasketare shown in Table 4. As a result, it was confirmed that when thecross-sectional shape of the nozzle was thus varied, the ratio h/w ofthe resultant gasket was suitably controlled.

EXAMPLE 6

The same procedure as in EXAMPLE 4 was repeated except that a nozzlehaving an isosceles triangular cross section (1.2×1.7 mm) was used, andthe extrusion pressure was changed as shown in Table 3, therebyobtaining a gasket. The details of a shape of the thus obtained gasketare shown in Table 4.

COMPARATIVE EXAMPLE 6

The gasket material PU#2 was applied onto a 0.4 mm-thick nickel-platedaluminum plate of a 2.5-inch HDD using the three-dimensional automaticcoating controlling apparatus 2, and then cured using an ultravioletcuring apparatus. Specifically, the gasket material was extruded underthe conditions shown in Table 3 using a nozzle having a circular crosssection (φ1.25 mm) without rotating the nozzle. The details of a shapeof the thus obtained gasket are shown in Table 4. As a result, it wasconfirmed that the ratio h/w was as low as 0.5, thereby failing toobtain a good gasket.

COMPARATIVE EXAMPLE 7

The same procedure as in EXAMPLE 4 was repeated except for using thethree-dimensional automatic coating controlling apparatus 1 of ascrew-extrusion type, thereby producing a gasket. Specifically, thegasket material was extruded under the conditions shown in Table 3 usinga nozzle having a circular cross section (φ1.25 mm) without rotating thenozzle. The details of a shape of the thus obtained gasket are shown inTable 4.

As a result, it was confirmed that the gasket material underwent ashearing force and, therefore, was deteriorated in viscosity, so thatthe ratio h/w thereof was as low as 0.6, thereby failing to obtain agood gasket.

COMPARATIVE EXAMPLE 8

The same procedure as in EXAMPLE 4 was repeated except that the gasketmaterial was extruded using a nozzle having a circular cross section(φ1.25 mm) without rotating the nozzle, thereby obtaining a gasket. Thedetails of a shape of the thus obtained gasket are shown in Table 4.

COMPARATIVE EXAMPLE 9

The same procedure as in EXAMPLE 4 was repeated except that the gasketmaterial was extruded without rotating the nozzle, thereby obtaining agasket. The details of a shape of the thus obtained gasket are shown inTable 4.

As a result, it was confirmed that when the major axis of the nozzle wasaligned with the moving direction, the obtained gasket portion had aheight of 1.5 mm, a line width of 1.0 mm and a ratio h/w of 1.5, whereaswhen the minor axis of the nozzle was aligned with the moving direction,the obtained gasket portion had a height of 0.9 mm, a line width of 1.8mm and a ratio h/w of 0.5, namely the resultant gasket was non-uniformin height. TABLE 3-1 Examples Three-dimensional and automatic Shape ofComparative Gasket controlling Extrusion extrusion Examples materialapparatus method orifice Example 4 PU#1 Apparatus 2 Pneumatic EllipticalExample 5 PU#1 Apparatus 2 Pneumatic Elliptical Example 6 PU#1 Apparatus2 Pneumatic Isosceles triangular Comparative PU#2 Apparatus 2 PneumaticCircular Example 6 Comparative PU#1 Apparatus 1 Screw Circular Example 7Comparative PU#1 Apparatus 2 Pneumatic Circular Example 8 ComparativePU#1 Apparatus 2 Pneumatic Elliptical Example 9

TABLE 3-2 Examples and Inner diameter Rotation or Extrusion Temperatureof Comparative of extrusion non-rotation pressure gasket materialExamples orifice of nozzle (kPa) (° C.) Example 4 1.1 × 1.8 Rotated 45055 Example 5 1.1 × 1.5 Rotated 450 55 Example 6 1.2 × 1.7 Rotated 500 55Comparative φ1.25 Non-rotated 330 Ordinary Example 6 temperatureComparative φ1.25 Non-rotated — Ordinary Example 7 temperatureComparative φ1.25 Non-rotated 450 55 Example 8 Comparative 1.1 × 1.8Non-rotated 450 55 Example 9

TABLE 4 Examples and Shape of gasket Comparative Cross-sectional Height(h) Line width (w) Examples shape (mm) (mm) h/w Example 4Semi-elliptical 1.5 1 1.5 Example 5 Semi-elliptical 1.3 1 1.3 Example 6Isosceles 1.5 1 1.5 triangular Comparative Semi-circular 1 2 0.5 Example6 Comparative Semi-circular 1 2 0.5 Example 7 Comparative Semi-circular1.1 1.4 0.79 Example 8 Comparative Semi-elliptical 1.5 to 0.9 1.0 to 1.81.5 to 0.5 Example 9

INDUSTRIAL APPLICABILITY

According to the present invention, a gasket having a large height canbe integrated with a cover member without using a mold and requiringblanking of sheets and bonding processes, and the obtained gasket can besuitably used as a gasket for small-size hard disc equipment.

1. A process for producing a gasket for hard disc equipment which isintegrated with a cover member by extruding a gasket material from anextrusion orifice of a three-dimensional automatic coating controllingapparatus onto the cover member and then curing the extruded gasketmaterial, wherein a ratio (h/w) of a height (h) of the gasket to a linewidth (w) thereof on a joint surface between the gasket and the covermember is in the range of 0.8 to 3.0 in a 80% or more portion of thegasket.
 2. The process according to claim 1, wherein the gasket materialis extruded from the extrusion orifice of the three-dimensionalautomatic coating controlling apparatus to form a first-stage gasket,and then the gasket material is further extruded on the first-stagegasket to obtain a multi-stage gasket.
 3. The process according to claim2, wherein the first-stage gasket is cured after formation thereof butbefore formation of the subsequent-stage gasket.
 4. The processaccording to claim 2, wherein the multi-stage gasket includes an n-stagegasket (n is an integer of 2 or more) having a length (w_(n)) of an axisthereof parallel with the cover member, and a (n−1)-stage gasket havinga length (w_(n−1)) of an axis thereof parallel with the cover member inwhich the lengths (w_(n)) and (w_(n−1)) satisfy a relationshiprepresented by the formula: w_(n−1)≧w_(n) in a 80% or more portion ofthe gaskets.
 5. The process according to claim 4, wherein themulti-stage gasket includes the n-stage gasket (n is an integer of 2 ormore) having the length (w_(n)) of an axis thereof parallel with thecover member, and the (n−1)-stage gasket having the length (w_(n−1)) ofan axis thereof parallel with the cover member in which the lengths(w_(n)) and (w_(n−1)) satisfy a relationship represented by the formula:w_(n−1)/w_(n)>1.1.
 6. The process according to claim 4, wherein then-stage gasket (n is an integer of 2 or more) has any of a circularshape, a semi-circular shape, an elliptical shape and a semi-ellipticalshape in cross section thereof, and a center of a cross section of then-stage gasket is offset from a center of a cross section of the(n−1)-stage gasket outwardly relative to a center of the cover member.7. The process according to claim 1, wherein the gasket material iscured while moving the extrusion orifice of the three-dimensionalautomatic coating controlling apparatus along a peripheral edge of thecover member, the extrusion orifice has a modified cross-sectional shapehaving a major axis and a minor axis and is rotated according to amoving direction thereof, and the minor axis of the extrusion orifice isalways kept substantially perpendicular to the moving direction.
 8. Theprocess according to claim 7, wherein the extrusion orifice has across-sectional shape selected from ellipse, semi-ellipse formed bycutting a part of ellipse along a line parallel with the minor axis,rhombus, quadrangle and triangle, and is rotated according to the movingdirection of the extrusion orifice such that a minor axis of ellipse, astraight line of semi-ellipse, a short diagonal line of rhombus, a shortside of quadrangle or a base of triangle is always kept substantiallyperpendicular to the moving direction.
 9. The process according to claim1, wherein the three-dimensional automatic coating controlling apparatusincludes an extruder selected from a pneumatic-type extruder, amechanical ram press-type extruder and a mechanical plunger-typeextruder, and a pressure used for extrusion of the gasket is in therange of 50 kPa to 1 MPa.
 10. The process according to claim 1, whereinthe gasket material has a viscosity of 50 to 1,000 Pa·s as measured at amolding temperature of the gasket and a shear rate of 1.0/s.
 11. Theprocess according to claim 1, wherein when a common logarithm (x) of ashear rate (s⁻¹) and a common logarithm (y) of a viscosity (Pa·s) of thegasket material is represented by the formula: y=−ax+b wherein a and bare positive numbers, the a value is 0.3 or more.
 12. The processaccording to claim 1, wherein the gasket material used has an interceptvalue of (5 Pa)^(1/2) or more (corresponding to a yield value of 5 Pa ormore) at which a line obtained by plotting a one-second power of a shearrate (s⁻¹) and a one-second power of a shear stress while varying theshear rate at a molding temperature thereof, intersects an axis of theone-second power of shear stress.
 13. The process according to claim 1,wherein the gasket material used has an intercept value of (30 Pa)^(1/2)or more (corresponding to a yield value of 30 Pa or more) on an axis ofthe one-second power of shear stress thereof.
 14. The process accordingto claim 1, wherein the gasket material used has an intercept value of(70 Pa)^(1/2) or more (corresponding to a yield value of 70 Pa or more)on an axis of the one-second power of shear stress thereof.
 15. Theprocess according to claim 1, wherein the gasket material has a hardnessof 50° or lower as measured by a durometer type-A hardness testaccording to JIS K
 6253. 16. The process according to claim 1, whereinthe gasket material contains, as a main component, at least one materialselected from the group consisting of urethanes, epoxy-based polymers,silicone, polyisobutylene, hydrogenated polyisobutylene, polybutadiene,hydrogenated polybutadiene, fluorine-containing rubbers and modifiedproducts thereof.
 17. The process according to claim 16, wherein thegasket material is an acrylic-modified urethane.
 18. The processaccording to claim 1, wherein the gasket material is cured byirradiating an activation energy ray thereto from an activation energyray irradiation apparatus.
 19. The process according to claim 18,wherein the activation energy ray irradiation apparatus is anultraviolet light irradiation apparatus, and an irradiation outletthereof is moved in association with the extrusion orifice of thethree-dimensional automatic coating controlling apparatus.
 20. Theprocess according to claim 19, wherein the irradiation outlet of theultraviolet light irradiation apparatus is revolved around the extrusionorifice of the three-dimensional automatic coating controlling apparatusby the same angle as an angle of rotation of the extrusion orificesimultaneously therewith.
 21. A gasket for hard disc equipment producedby the process as claimed in claim 1, which is applied to a hard discequipment having a size of less than 3.5 inch (88.9 mm).